In medical science, the endoscopy of a colon by means of an endoscope is referred to as coloscopy and the respective specifically designed endoscopes are known as coloscopes. A coloscope comprises an optical system usually connected with a display device to allow for diagnosis by a physician. Insertion of a coloscope in the colon is sensed as being intrusive or even painful by many patients and always, in particular, in the case of enteritis/colitis, includes a risk of penetrating the intestinal wall.
As an alternative virtual coloscopy has been developed during which no physical coloscope has to be inserted in the patient's body any longer. Instead of coloscopes methods and apparatuses used in computer tomography/magnetic resonance imaging are used to detect data and to visualize the data. Progress of virtual coloscopy has significantly been advanced by the fact that due to the increased computational power of present day computers expensive image processing can readily be carried out.
With virtual coloscopy, a large number of spatially resolved parallel slices is recorded by a tomographic means. Each of these slices corresponds to a set of two-dimensional image data. These data sets are numerically converted to a three-dimensional image data set. From this three-dimensional image, data set two-dimensional image data can be calculated again that are independent of the direction of the original slice (cut), e.g., oblique to this direction. Usually the two- and three-dimensional image data are reproduced by means of a two-dimensional display device (monitor, photo, etc.), namely they are visualized as sectional views (i.e. all of the displayed pixels belong to one intersection plane) or as pseudo-three-dimensional images that create a three-dimensional impression in a way similar to conventional photography (the pixels do not originate from a plane surface).
It should be noted that it could not be decided a priori which one of the views is most suitable for the most accurate diagnosis. Whereas the (pseudo)-three-dimensional data representations are rather demonstrative due to the spatial impression given and thus, are helpful for the spatial orientation, it is particularly for these views that possible anomalies as lesions are hidden by tissue (e.g. by a colon fold) and therefore are invisible. Contrarily, in sectional views such a concealing does not occur. However, the sectional views are not very helpful for a medical treatment that usually requires a three-dimensional coordination.